The P2X7 receptor is a ligand-gated ion channel and is present on a variety of cell types, largely those known to be involved in the inflammatory and/or immune process, specifically, macrophages and monocytes in the periphery and predominantly in glial cells (microglia and astrocytes) of the CNS. (Duan and Neary, Glia 2006, 54, 738-746; Skaper et al., FASEB J 2009, 24, 337-345; Surprenant and North, Annu. Rev. Physiol. 2009, 71, 333-359). Activation of the P2X7 receptor by extracellular nucleotides, in particular adenosine triphosphate, leads to the release of proinflammatory cytokines IL-1β and IL-18 (Muller, et. al. Am. J. Respir. Cell Mol. Biol. 2011, 44, 456-464), giant cell formation (macrophages/microglial cells), degranulation (mast cells) and L-selectin shedding (lymphocytes) (Ferrari et al., J. Immunol. 2006, 176, 3877-3883; Surprenant and North, Annu. Rev. Physiol. 2009, 71, 333-359). P2X7 receptors are also located on antigen-presenting cells (keratinocytes, salivary acinar cells (parotid cells)), hepatocytes, erythrocytes, erythroleukaemic cells, monocytes, fibroblasts, bone marrow cells, neurones, and renal mesangial cells.
The importance of P2X7 in the nervous system arises primarily from experiments using P2X7 knock-out mice. These mice demonstrate the role of P2X7 in the development and maintenance of pain as these mice were protected from the development of both adjuvant-induced inflammatory pain and partial nerve ligation induced neuropathic pain (Chessell et al., Pain 2005, 114, 386-396). In addition P2X7 knock-out mice also exhibit an anti-depressant phenotype based on reduced immobility in forced swim and tail suspension tests (Basso et al., Behav. Brain Res. 2009, 198, 83-90.). Moreover, the P2X7 pathway is linked to the release of the pro-inflammatory cytokine, IL-1β, which has been linked to precipitation of mood disorders in humans (Dantzer, Immunol. Allergy Clin. North Am. 2009, 29, 247-264; Capuron and Miller, Pharmacol. Ther. 2011, 130, 226-238). In addition, in murine models of Alzheimer's disease, P2X7 was upregulated around amyloid plaques indicating a role of this target in such pathology as well (Parvathenani et al., J. Biol. Chem. 2003, 278, 13309-13317).
In view of the clinical importance of P2X7, the identification of compounds that modulate P2X7 receptor function represents an attractive avenue into the development of new therapeutic agents. Such compounds are provided herein.